Polymeric foam containing alumina boehmite

ABSTRACT

Prepare a polymeric foam by expanding a foamable polymer composition comprising alumina boehmite.

CROSS REFERENCE STATEMENT

This application claims the benefit of U.S. Provisional Application No.61/163,891, filed Mar. 27, 2009, the entire content of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polymeric foam and a process forpreparing polymeric foam.

2. Description of Related Art

Thermally insulating polymeric foam is commonplace in our world today.Thermally insulating polymeric foam sheets are available in most supplycenters for implementation in structural building. Current energy costsand desires by consumers for more comfortable homes continually drivedevelopment of more desirable thermally insulating polymeric foams. Oneparamount driver is to reduce the thermal conductivity through polymericfoam.

Inclusion of an infrared attenuator in polymeric foam is one means ofdecreasing thermal conductivity through the foam. Infrared attenuatorsin polymeric foam inhibit the penetration of infrared energy through thefoam and thereby help to retain heat on one side of the foam. Commoninfrared attenuators include carbon black, graphite and titanium dioxide(TiO2). However, each of these infrared attenuators creates challengesin manufacturing desirable thermally insulating polymeric foam.

Carbon black, graphite and titanium dioxide (TiO₂) all have particlesizes of approximately one micrometer or smaller. Particulate additivesof that size act as nucleating agents during manufacture of polymericfoam. At a given loading weight, an additive with such a small particlesize and large surface area provides a multitude of nucleating siteseach of which can induce formation of a cell during foam expansion. As aresult, carbon black, graphite and TiO₂ all promote formation of smallcell sizes. Small cell sizes are undesirable in the process of makingthermally insulating foam because small cell sizes lead to a high foamdensity, which becomes economically unfavorable. In that regard, aninfrared attenuator having a larger particle size is desirable. At thesame loading weight, an additive having a larger size provides fewernucleating sites than a smaller sized additive. Yet, larger particlesized fillers can promote open cell structures in the polymeric foam. Aparticle that has a size larger than the cell wall between to cells cancause rupturing of the wall between the cells and promote open cellstructure throughout the foam, which is also undesirable for thermallyinsulating foam. Cell walls of thermally insulation polymeric foam aregenerally 0.8 to 3 microns thick.

Carbon black and graphite have a characteristic black or grey color.These additives act as pigments that cause polymeric foam containingcarbon black and graphite to be black or grey. This can be undesirableif there is a desire to have a color other than black or grey because itis difficult to modify the color of black or grey foam much by additionof other pigments. Some consumers may desire white foam for its cleanappearance. Some manufactures may desire thermally insulating foam thatthey can pigment to a certain color representative of their products, acolor that is not grey or black. Carbon black and graphite becomeundesirable additives in these situations.

Titanium dioxide (TiO₂) is white in color and therefore does not sufferfrom the challenging black and grey color of carbon black and graphite.However, titanium dioxide has a small particle size that promotesnucleation. Moreover, titanium dioxide is such an efficient whitepigment that it also makes it difficult to color foam to a particularnon-white color because the TiO₂ washes out the non-white pigment color.

It is desirable to find a thermally insulating additive for polymericfoam that does not act as a nucleator as much as do carbon black,graphite and TiO₂ yet that allows for formation of closed cell foam.Moreover, it is desirable to find such a thermally insulating additivethat has minimal affect on the color of polymeric foam and thatminimally interferes with use of pigments in coloring the polymericfoam.

BRIEF SUMMARY OF THE INVENTION

The present invention solves one or more problems associated withproviding a polymeric foam containing a thermally insulating additivethat does not act as a nucleator as much as carbon black, graphite andTiO₂ yet that allows for formation of closed cell foam while havingminimal effect on the color of the polymeric foam and that minimallyinterferes with use of pigments in coloring the polymeric foam.

The present invention results from exploring alumina boehmite as anadditive in polymeric foam. Alumina boehmite is typically used as acatalyst in applications such as chemical catalysts, automotivewashcoats catalysts, binder and support catalysts and for use as sol-gelabrasives and polishing compounds. Unexpectedly and surprisingly,alumina boehmite acts as a thermally insulating additive in polymericfoam. Moreover, alumina boehmite does not cause undesirably small cellsizes and has a particle size larger than carbon black yet allowsformation of closed cell foam. Alumina boehmite also has minimal affecton the color of polymeric foam and has little effect on the pigmentingof polymeric foam.

In a first aspect, the present invention is a process for preparingpolymeric foam comprising the following steps: (a) providing a foamablepolymer composition comprising a blowing agent dispersed in a polymermatrix, the polymer matrix having a softening temperature; and (b)exposing the foamable polymer composition while at a temperature at orabove the softening temperature of the polymer matrix to an environmenthaving a pressure low enough to cause the foamable polymer compositionto expand into a polymeric foam; wherein the foamable polymercomposition further comprises alumina boehmite dispersed in the polymermatrix.

Some desirable embodiments of the first aspect can have any one or anycombination of more than one of the following additionalcharacteristics: the alumina boehmite is present in the polymer matrixat a concentration in a range of 0.1 to 30 weight-percent based onpolymer matrix weight; the alumina boehmite has a nitrate concentrationof less than 3.0 weight percent; 50 weight-percent of all the polymersin the polymer matrix are alkenyl aromatic polymers; at least 95weight-percent of all polymers in the polymer matrix are selected frompolystyrene homopolymer and styrenic copolymers; the blowing agentcomprises carbon dioxide; the blowing agent comprise carbon dioxide andat least one of iso-butane and water; and the polymeric foam has an opencell content of five percent or less.

In a second aspect, the present invention is polymeric foam comprising apolymer matrix defining a plurality of cells dispersed therein andfurther comprising alumina boehmite dispersed within the polymer matrix.

Some desirable embodiments of the second aspect can further have any oneor any combination of more than one of the following characteristics:the polymeric foam is extruded polymeric foam that is free of a networkof polymer skins defining foam beads; the alumina boehmite is present ata concentration in a range of 0.1 to 30 weight percent based on totalpolymer weight in the polymer matrix; the alumina boehmite is present ata concentration in a range of 0.5 to 5 weight-percent based on polymercomposition weight; the alumina boehmite has a nitrate concentration ofless than three weight percent; more than 50 weight-percent of all thepolymers in the polymer matrix are alkenyl aromatic polymers; thealkenyl aromatic polymer is selected from polystyrene homopolymer andstyrenic copolymers; and the polymeric foam has an open cell content offive percent or less.

The process of the present invention is useful for preparing thepolymeric foam of the present invention. The foam of the presentinvention is useful as a thermal insulating material.

DETAILED DESCRIPTION OF THE INVENTION

All ranges herein include endpoints unless otherwise noted.

ASTM refers to American Society for Testing and Materials. ISO refers toInternational Organization for Standardization. EN refers to EuropeanNorm. DIN refers to Deutsches Institute für Normung e.V. ASTM, ISO, ENand DIN test methods refer to the method as of the year in thehyphenated suffix of the method number or, if there is no hyphenatedsuffice, the most recent method published prior to the priority date ofthe present document.

In the process of the present invention provide a foamable polymercomposition comprising a blowing agent dispersed in a polymer matrix.

The blowing agent can be any blowing agent composition suitable for usein preparing polymeric foam now or in the future. For example, theblowing agent can be any one or any combination of more than one blowingagent selected from a group consisting of: inorganic gases such ascarbon dioxide, argon, nitrogen, and air; organic blowing agents such aswater, aliphatic and cyclic hydrocarbons having from one to nine carbonsincluding methane, ethane, propane, n-butane, iso-butane, n-pentane,iso-pentane, neo-pentane, cyclobutane, and cyclopentane; fully andpartially halogenated alkanes and alkenes having from one to fivecarbons, preferably that are chlorine-free (e.g., difluoromethane(HFC-32), perfluoromethane, ethyl fluoride (HFC-161),1,1,-difluoroethane (HFC-152a), 1,1,1-trifluoroethane (HFC-143a),1,1,2,2-tetrafluoroethane (HFC-134), 1,1,1,2 tetrafluoroethane(HFC-134a), pentafluoroethane (HFC-125), perfluoroethane,2,2-difluoropropane (HFC-272fb), 1,1,1-trifluoropropane (HFC-263fb),1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea),1,1,1,3,3-pentafluoropropane (HFC-245fa), and1,1,1,3,3-pentafluorobutane (HFC-365mfc)); aliphatic alcohols havingfrom one to five carbons such as methanol, ethanol, n-propanol, andisopropanol; carbonyl containing compounds such as acetone, 2-butanone,and acetaldehyde; ether containing compounds such as dimethyl ether,diethyl ether, methyl ethyl ether; carboxylate compounds such as methylformate, methyl acetate, ethyl acetate; carboxylic acid and chemicalblowing agents such as azodicarbonamide, azodiisobutyronitrile,benzenesulfo-hydrazide, 4,4-oxybenzene sulfonyl semi-carbazide,p-toluene sulfonyl semi-carbazide, barium azodicarboxylate,N,N′-dimethyl-N,N′-dinitrosoterephthalamide, trihydrazino triazine andsodium bicarbonate.

In one desirable embodiment, the blowing agent is selected from a groupconsisting of carbon dioxide, hydrocarbons having from one to fivecarbons and water. The blowing agent can contain carbon dioxide, carbondioxide and water, carbon dioxide and one or more of the hydrocarbons,or carbon dioxide with water and one or more of the hydrocarbons. Aparticularly desirable hydrocarbon for use as the, or as one of the,hydrocarbons is iso-butane. Particular examples of this desirableembodiment contain 40-100 wt % carbon dioxide, 0-60 wt % iso-butane and0-20 wt % water, with wt % based on total blowing agent weight.

Another particularly desirable blowing agent is1,1,1,2-tetrafluoroethane (HFC-134a). HFC-134a can be included in thedesirable embodiments containing carbon dioxide and optionally water andoptionally one or more hydrocarbon (particularly iso-butane). Anotherdesirably blowing agent combination includes carbon dioxide at aconcentration of 10-90 wt %, carbon dioxide at a concentration of 0-50wt %, iso-butane at a concentration of 0-60 wt %, ethanol at aconcentration of 0-50 wt % and water at a concentration of 0-20 wt %,with wt % based on total blowing agent weight.

Blowing agent is generally present in the foamable polymer compositionat a concentration of 0.05 to 0.35, preferably 0.08 to 0.25, and mostpreferably 0.10 to 0.20 moles per hundred grams of polymer in thepolymer matrix.

The polymer matrix is a continuous phase comprising one or a combinationof more than one polymer. Typically, most (more than 50 percent byweight) of the polymers in the polymer matrix are thermoplasticpolymers. Thermoplastic polymers can account for 70 weight-percent (wt%), 80 wt %, 90 wt % or even 100 wt % of the polymers in the polymermatrix. Suitable thermoplastic polymers include olefinic polymers,alkenyl-aromatic homopolymers and copolymers comprising both olefinicand alkenyl aromatic components. Examples of suitable olefinic polymersinclude homopolymers and copolymers of ethylene and propylene.

Desirably, the polymer matrix comprises one or more than onealkenyl-aromatic polymer. Alkenyl-aromatic polymer is desirably 50 wt %or more, preferably 70 wt % or more and can be 80 wt % or more, 90 wt %or more, 95 wt % or more and can even be 100 wt % of all the polymers inthe polymer matrix. An alkenyl-aromatic polymer is a polymer containingalkenyl aromatic monomers polymerized into the polymer structure.Alkenyl-aromatic polymer can be homopolymers, copolymers or blends ofhomopolymers and copolymers. Alkenyl-aromatic copolymers can be randomcopolymers, alternating copolymers, block copolymers or any combinationthereof and my be linear, branched or a mixture thereof.

Styrenic polymers are particularly desirably alkenyl-aromatic polymers.Styrenic polymers have styrene monomer polymerized in the polymerbackbone and include styrene homopolymer, copolymer and blends thereof.Polymeric foams comprising more than 50 wt % styrenic polymers areExtruded Polystyrene, or XPS, foam. The foam of the present invention isdesirably XPS foam.

Desirably, styrenic homopolymer for use in the present invention has aweight average molecular weight (Mw) in a range of 100,000 to 500,000grams per mole, preferably from 130,000 to 400,000 grams per mole. Themolecular weight distribution (Mw/Mn) is in a range from 1.0 to 10.0 andpreferably in a range of 1.5 to 5.0, and most preferably from 2.0 to 4.0

Examples of styrenic copolymers suitable for the present inventioninclude copolymers of styrene with one or more of the following: acrylicacid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid,acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate,isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetateand butadiene.

Styrene-acrylonitrile copolymer (SAN) is a particularly desirablealkenyl-aromatic polymer for use in the present invention because of itsease of manufacture and monomer availability. SAN copolymer can be ablock copolymer or a random copolymer, and can be linear or branched.SAN provides greater water solubility than polystyrene homopolymer,thereby facilitating use of an aqueous blowing agent. SAN also hashigher heat distortion temperature than polystyrene homopolymer, whichprovides for foam having a higher use temperature than polystyrenehomopolymer foam. Desirable embodiments of the present process employpolymer compositions that comprise, even consist of SAN. Thealkenyl-aromatic polymer, even the polymer matrix itself may comprise orconsist of a polymer blend of SAN with another polymer such aspolystyrene homopolymer.

Desirably, SAN for use in the present invention has a weight averagedmolecular weight (Mw) in a range of 50,000 to 300,000 grams per mole,preferably from 100 to 200,000 grams per mole. The molecular weightdistribution (Mw/Mn) is desirably in a range of 1.0 to 10, preferably ina range of 1.2 to 5.0 and most preferably in a range of 1.5 to 3.0.

The foamable polymer composition further comprises alumina boehmitedispersed within the polymer matrix. Alumina boehmite is an aluminumoxide hydroxide mineral that is dimorphous with diaspore. Aluminaboehmite crystallites are leaflet or rectangular shaped and the shape ischaracterized by a high aspect ratio. Alumina boehmite has crystallitesizes of 2 to 200 nanometers (nm). Alumina boehmite for use in thepresent invention can haves a crystallite size (diameter) of 2 nm orgreater, even 6 nm or greater and has a crystallize size of 200 nm orless, and can have a size of 100 nm or less, even 60 nm or less. Aluminaboehmite is typically used as a catalyst in applications such aschemical catalysts, automotive washcoats catalysts, binder and supportcatalysts and for use as sol-gel abrasives and polishing compounds,viscosifiers and anti-skid agents (see, for example, the description ofHiQ® boehmite alumina from BASF athttp://www.catalysts.basf.com/main/process/adsorbents/alumina_based_adsorbent_technologies/hiq_boehmite_alumina.be).

The alumina boehmite can be organically modified and may contain a highconcentration of nitrate as a result of being prepared or synthesizedwith nitric acid. The alumina boehmite desirably has a nitrate contentof 3.0 wt % or less based on total alumina boehmite weight in order toensure it has suitable chemical and thermal stability for temperaturesof 180° C. or higher, which are possible in extrusion foaming processes.When the nitrate content exceeds 3.0%, decomposition of the aluminaboehmite can occur at elevated temperatures and cause yellowing in thepolymeric foam.

Surprisingly, research leading to the present invention discovered thatthe alumina boehmite acts as an infrared attenuator in polymeric foambut without having the strong and detrimental nucleating effect ofcarbon black, graphite and titanium dioxide. Moreover, alumina boehmitesurprisingly has little effect on pigmentation of the polymeric foam,unlike carbon black, graphite and titanium dioxide.

The foamable polymer composition desirably contains at least 0.1 wt %alumina boehmite based on polymer matrix weight in order to achieveeffective infrared attenuation in the resulting polymeric foam.Preferably, the alumina boehmite is present at a concentration of 0.2 wt% or more, more preferably at a concentration of 0.5 wt % or more basedon polymer matrix weight in order to achieve optimal infraredattenuation. Typically, alumina boehmite is present at a concentrationof 30 wt % or less, preferably 20 wt % or less and still more preferably10 wt % or less based on polymer matrix weight.

The foamable polymer composition can optionally contain additionallyadditives, typically dispersed within the polymer matrix. Commonadditives include any one or combination of more than one of thefollowing: infrared attenuating agents (for example, carbon black,graphite, metal flake, titanium dioxide); clays such as naturalabsorbent clays (for example, kaolinite and montmorillonite) andsynthetic clays; nucleating agents (for example, talc and magnesiumsilicate); flame retardants (for example, brominated flame retardantssuch as brominated polymers, hexabromocyclododecane, phosphorous flameretardants such as triphenylphosphate, and flame retardant packages thatmay including synergists such as, or example, dicumyl and polycumyl);lubricants (for example, calcium stearate and barium stearate); and acidscavengers (for example, magnesium oxide and tetrasodium pyrophosphate).

The polymer matrix has a softening temperature. At and above itssoftening temperature a polymer matrix is capable of being mixed withadditives and blowing agents.

“Softening temperature” (T_(s)) for a polymer matrix whose polymers areall semi-crystalline is the melting temperature for the polymer matrix.“Melting temperature” (T_(m)) for a semi-crystalline polymer is thetemperature half-way through a crystalline-to-melt phase change asdetermined by differential scanning calorimetry (DSC) upon heating acrystallized polymer at a specific heating rate. Determine T_(m) for asemi-crystalline polymer according to the DSC procedure in ASTM methodE794-06. Determine T_(m) using a heating rate of 10 degrees Celsius (°C.) per minute. If the polymer component only contains miscible polymersand only one crystalline-to-melt phase change is evident in its DSCcurve, then T_(m) for the polymer matrix is the temperature half-waythrough the phase change. If multiple crystalline-to-melt phase changesare evident in a DSC curve due to the presence of immiscible polymers,then T_(m) for the polymer matrix is the T_(m) of the continuous phasepolymer. If more than one polymer is continuous and they are notmiscible, then the T_(m) for the polymer matrix is the highest T_(m) ofthe continuous phase polymers.

The softening temperature for a polymer matrix whose polymers areamorphous is the glass transition temperature for the polymer matrix.“Glass transition temperature” (T_(g)) for a polymer component is asdetermined by DSC according to the procedure in ASTM method E1356-03. Ifthe polymer matrix contains only miscible polymers and only one glasstransition phase change is evident in the DSC curve, then T_(g) of thepolymer matrix is the temperature half-way through the phase change. Ifmultiple glass transition phase changes are evident in a DSC curve dueto the presence of immiscible amorphous polymers, then T_(g) for thepolymer matrix is the T_(g) of the continuous phase polymer. If morethan one amorphous polymer is continuous and they are not miscible, thenthe T_(g) for the polymer matrix is the highest T_(g) of the continuousphase polymers.

If the polymer matrix contains a combination of semi-crystalline andamorphous polymers, the softening temperature of the polymer matrix isthe softening temperature of the continuous phase polymer component. Ifthe semi-crystalline and amorphous polymer phases are co-continuous,then the softening temperature of the polymer matrix is the highersoftening temperature of the two phases.

The present invention further includes exposing the foamable polymercomposition to an environment having a pressure low enough to cause thefoamable polymer composition to expand into a polymeric foam while thefoamable polymer composition is at a temperature at or above thesoftening temperature of the polymer matrix. The broadest scope of thepresent invention captures many different foaming processes which maydiffer in the procedure for carrying out this step of the process. Inthe broadest scope, the present invention encompasses all methods ofcarrying out both providing the foamable polymer composition andexposing the foamable polymer composition to a pressure low enough tocause the foamable polymer composition to expand into a polymeric foamwhile the polymer composition is at a temperature at or above thesoftening temperature of the polymer matrix.

Examples of suitable foaming processes include expanded polymer beadprocesses and extrusion processes.

Expanded bead foam processes are batch processes that require preparinga foamable polymer composition comprising granules comprisingthermoplastic polymer matrix that has blowing agent dispersed within thegranule. Incorporate the blowing agent into the polymer granule in anymanner including imbibing granules of thermoplastic polymer compositionwith a blowing agent under pressure. Each granule (or bead) is, in asense, a foamable polymer composition. Often, though not necessarily,the foamable beads undergo at least two expansion steps. An initialexpansion occurs by heating the granules above the softening temperatureof the polymer matrix of the granules and allowing the blowing agent toexpand the beads in an atmosphere of pressure low enough to allowexpansion. A second expansion is often done with multiple beads in amold by exposing the beads to steam to further expand the beads and fusethem together. A bonding agent is commonly coated on the beads beforethe second expansion to facilitate bonding of the beads together.

Expanded bead foam comprises multiple expanded polymer beads affixed toone another. As a result, a characteristic feature of expanded bead foamis a continuous network of polymer skins throughout the foam thatdefines each expanded bead and that generally interconnects all of thesurfaces of the polymeric foam. The polymer skin network corresponds tothe surface of each individual bead and encompasses relatively small andlocalized groups of cells throughout the foam. The polymer skin networkis of higher density than the portion of foam containing groups of cellsthat the network encompasses, including cell walls.

Extrusion processes are more desirable than expanded bead foam processesbecause produce polymeric foam that is free of such an extensiveinternal network of bead skins that can increase thermal conductivitythrough the polymeric foam. Extrusion processes include coalesced strandfoam processes and individual foam sheet and board processes (that is,processes that extrude a foam that is free from multiple foamed elementsaffixed to one another). Extrusion processes can be semi-continuous,such as an accumulator extrusion process, or continuous, meaning theprocess is continuous from addition of the components into an extruderto formation of the polymeric foam without delay in-between

In an extrusion process, provide the foamable polymer composition in anextruder at the initial temperature and initial pressure and extrudethrough a foaming die into an atmosphere if pressure lower than theinitial pressure to allow the foamable polymer composition to expand.One way to prepare the foamable polymer composition is to feed polymerinto the extruder and heat to the initial temperature within theextruder. Addition of alumina boehmite and any additional fillers intothe extruder can occur simultaneously with the polymer, downstream inthe extruder from addition of the polymer or a combination of both.Generally, inject blowing agent at the initial pressure into theextruder downstream from the polymer addition and mix with the polymerand alumina boehmite and any other additive to form the foamable polymercomposition. The resulting combination of polymer, additive(s) andblowing agent form a foamable polymer composition.

An accumulation extrusion process comprises: 1) mixing a thermoplasticmaterial and a blowing agent composition to form a foamable polymercomposition; 2) extruding the foamable polymer composition into aholding zone maintained at a temperature and pressure which does notallow the foamable polymer composition to foam; the holding zone has adie defining an orifice opening into a zone of lower pressure at whichthe foamable polymer composition foams and an openable gate closing thedie orifice; 3) periodically opening the gate while substantiallyconcurrently applying mechanical pressure by means of a movable ram onthe foamable polymer composition to eject it from the holding zonethrough the die orifice into the zone of lower pressure, and 4) allowingthe ejected foamable polymer composition to expand to form the foam.U.S. Pat. No. 4,323,528, incorporated herein by reference, disclosessuch a process in a context of making polyolefin foams.

In a continuous extrusion process the foamable polymer compositioncontinues through the extruder and is expelled, generally through afoaming die, into an atmosphere having a pressure lower than the initialpressure and sufficiently low to allow for foaming of the foamablepolymer composition all without delay or interruption.

In a coalesced strand foam process, expel the foamable polymercomposition through a foaming die having a plurality of openings toextrude multiple strands of foamable polymer composition simultaneously.As the strands expand they contact one another and become affixed to oneanother to form a coalesced strand foam. Coalesced strand foams aresimilar to expanded bead from in that they both have a skin networkwithin the foam. However, coalesced strand foams are distinct fromexpanded bead foam in that the skin network does not surround smalllocalized beads of cells but rather extend the full length of a foam andremain open on the ends.

In an extrusion process that prepares an individual foam sheet andboard, extrude the foamable polymer composition through a foaming diehaving a single opening. An individual foam sheet or board made by anextrusion process is free of a skin network within the foam that has adensity higher than the cell walls.

The polymeric foam resulting from the process of the present inventionis a polymeric foam of the present invention. The polymeric foamcomprises a polymer matrix that defines a plurality of cells and thatcontains alumina boehmite dispersed within it. The polymer matrix of thepolymeric foam is as described for the foamable polymer composition. Thealumina boehmite is also as described for the foamable polymercomposition, including preferred concentrations.

The foam of the present invention desirably has a density of 200kilograms per cubic meter (kg/m³) or less, preferably 100 kg/m³ or less,still more preferably 64 kg/m³ or less. Lower density foams aredesirable to reduce cost of manufacture and transportation as well asfor ease of handling. Typically, the polymeric foam of the presentinvention has a density of 8 kg/m³ or higher and desirably has a densityof 16 kg/m³ or higher, preferably 24 kg/m³ or higher in order to ensuremechanical integrity during handling. Determine foam density accordingto the method of ISO 845-95.

The foam of the present invention desirably has an average cell size of0.05 millimeters (mm) or more, preferably 0.1 mm or more, still morepreferably 0.2 mm or more and generally has a cell size of 5.0 mm orless, typically 1.0 mm or less. Determine average cell size according toASTM method D-3576.

The open cell content of the foam of the present invention is desirably30% or less, preferably 10% or less, still more preferably 5% or less,even more preferably 2% or less. The open cell content can be 1% or lessor even 0%. Determine open cell content according the method of ASTMD6226-05.

The polymeric foam of the present invention is desirably a thermallyinsulating material having a thermal conductivity of 40 milliWatts permeter*Kelvin (Mw/m*K) or less, preferably 35 mW/m*K or less, still morepreferably 33 mW/m*K or less. Determine thermal conductivity accordingto the method of EN 8301.

EXAMPLES Preparation

Control Foam

Prepare a control sample without any infrared attenuating agents byfirst dry blending 100 weight-parts of polystyrene resin composed of 80wt % low Mw polystyrene (Mw=145,000 g/mol, Mw/Mn=3.3) and 20 wt % highMw polystyrene (Mw=200,000 g/mol, Mw/Mn=2.7) with 0.1 weight partsbarium stearate, 0.2 weight parts copper phthalocyanine blue pigment (ina 20 wt % concentrate in polystyrene) and 0.2 weight parts polyethyleneand feed the blend in to a 50 millimeter (mm) extruder that heats theblend to 200° C. and mixes it thoroughly. While in the extruder, add ablowing agent consisting of 4 weight parts carbon dioxide and 1.5 weightparts iso-butane at a pressure that precludes foaming (13-25 megapascalsfor mixing) to form a foamable polymer composition. After blending thefoamble polymer composition, reduce its temperature to approximately127° C. and extrude it through a slit die into atmospheric pressure (101kilopascals) and ambient temperature (23° C.) and allow it to form intorectangular polymeric foam. Die pressure is in a range of 4-12megapascals.

Comparative Examples A-C

Prepare the Comparative Examples (Comp Exs) in like manner as theControl except:

Comp Ex A

Omit the blue pigment and in the dry blend include carbon black havingan average particle size of approximately 250 nanometers (for example,THERMAX®-991, THERMAX is a trademark of Cancarb Co.). Add the carbonblack into the dry blend as a compounded concentrate that is 60 wt %polystyrene. Comp Ex A(i) contains 2.5 wt % carbon black and Comp ExA(ii) contains 5 wt % carbon black.

Comp Ex B

Omit the blue pigment and in the dry blend include graphite having anaverage particle size of approximately 3.0 micrometers (for example,UF-1 from Kopfmuel GmbH). Add the graphite into the dry blend as acompounded concentrate that is 70 wt % polystyrene. Comp Ex B(i)contains 2.5 wt % graphite and Comp Ex B(ii) contains 5 wt % Graphite.

Comp Ex C

In the dry blend include organic coated titanium dioxide having anaverage particle size of approximately 220 nanometers (for example,Ti-PURE® R-104, Ti-PURE is a trademark of E.I.Du Pont De Nemours andCompany). Add the coated titanium dioxide into the dry blend as acompounded concentrate that is 50 wt % polystyrene. Comp Ex C(i)contains 2.5 wt % titanium dioxide and Comp Ex C(ii) contains 5 wt %titanium dioxide.

Examples 1 and 2

Prepare Examples (Exs) in like manner as the Control Foam except:

Ex 1

In the dry blend include alumina boehmite having an average particlesize of approximately 15 microns (for example, PURAL®-NF, PURAL is atrademark of Sasol Germany GmbH). Add the alumina boehmite into the dryblend as a compounded concentrate that is 80% polystyrene). Ex 1(i)contains 2.5 wt % alumina boehmite and Ex 1(H) contains 5 wt % aluminaboemite.

Ex 2

In the dry blend include alumina boehmite having an average particlesize of approximately 40 microns (for example, DISPAL® 25F4, DISPAL is atrademark of Sasol North America, Inc.). Add the alumina boehmite intothe dry blend as a compounded concentrate that is 80% polystyrene). Ex2(i) contains 2.5 wt % alumina boehmite and Ex 2(ii) contains 5 wt %alumina boemite.

Properties

Table 1 lists typical properties of the Control, Comp Exs and Ex.Determine density according to the method of ISO 845-95. Determine OpenCell Content according to the method of ASTM D6226-05. Determine averagecell size according to the method of ASTM D-3576. Determine thermalconductivity according to the method of EN8301.

Characterize the color of the foam using the L*a*b* (CIELAB) colorspace. CIE L*a*b* (CIELAB) is a color spaced specified by theInternational Commission on Illumination (Commission Internationaled'Eclairage). Characterize the foam samples in terms of the CIE L*a*b*color space coordinates using a Minolta Chroma Meter CR210 colormeter.The L* coordinate represents the lightness of the color (L* of 0 isblack and L* of 100 is diffuse white). The a* coordinate corresponds toa range between red/magenta and green (more negative a* valuescorrespond to more green while more positive a* values correspond tomore red/magenta). The b* coordinate corresponds to a color rangebetween yellow and blue (more negative b* values correspond to more bluewhile more positive b* values correspond to more yellow).

TABLE 1 Control Comparative Example Example Property Sample A(i) A(ii)B(i) B(ii) C(i) C(ii) 1(1) 1(ii) 2(i) 2(ii) Amount of 0 2.5 5 2.5 5 2.55 2.5 5 2.5 5 Infrared Attenuator (weight-parts) Thickness 24 22 22 1919 21 23 28 26 28 28 (mm) Density 36.5 37.4 38.8 38 39.2 37.3 36.8 33.835.0 33.7 33.9 (kg/m³) Open Cell 1.0 1.4 0.5 5.3 12.8 0.5 0.2 1.5 0.71.2 0.0 Content (%) Cell Size 0.14 0.10 0.11 0.08 0.06 0.10 0.15 0.200.19 0.19 0.19 (mm) Thermal 32.6 31.1 30.1 29.3 29.5 31.5 30.6 30.5 30.030.8 30.6 Conductivity (mW/m*K at 10° C. after 30 days) L* 85.6 59.355.4 63.0 59.1 89.0 89.0 83.3 85.2 85.5 87.2 a* −5.7 0.1 −0.1 0.2 0.2−5.2 −5.1 −6.5 −5.8 −6.0 −7.3 b* −16.5 −1.7 −1.7 −1.3 −0.9 −13.3 −12.2−17.9 −15.6 −15.4 −14.2Comparing the characteristics of the Control Sample, Comp Examples andExamples the following observations are evident:

-   -   Alumina boehmite acts as an infrared attenuator as is evident by        a reduction in thermal conductivity in each of the Examples.    -   The alumina boehmite examples all illustrate in increase in cell        size relative to the Control, just the opposite effect expected        by nucleation. In contrast, carbon black, graphite and titanium        dioxide all tend to induce a decrease the cell size of the        polymeric foam (C(ii) excepted, which remained approximately        equal to the control).    -   The Control Foam and the foam containing alumina boehmite        (Examples 1 and 2) have nearly identical coloring. In contrast,        the foams produced with carbon black (A foams) and graphite (B        foams) are dramatically different in color—darker, redder and        much less blue. The foams produced with the coated titanium        dioxide are whiter, less green and less blue than the control.        The alumina boehmite did not dramatically affect the color of        the foam while the other infrared attenuators did.

These polymeric foams illustrate surprising behavior of alumina boehmiteas an infrared attenuating agent in polymeric foam.

Example 3 Nitrated Alumina Boehmite

Prepare Example 3 in like manner as Exs 1 and 2 with the followingdifferences:

-   -   (1) Use as the alumina boehmite DISPERAL® P2 (from Sasol North        America, Inc.), which has a nitrate concentration of 3.4 to 4.0        wt %.    -   (2) Use a 0.75 inch (20 millimeter) extruder;    -   (3) Use 3.5 pph carbon dioxide; and    -   (4) Omit the blue pigment.

At alumina boehmite concentrations of 4, 7 and 10 weight-parts allresulted in an undesirable decrease in cell size and an undesirableyellowing of the polymeric foam. The decrease in cell size and yellowingare likely a result of thermal degradation of the alumina boehmiteduring the foam manufacturing process. This Example illustrates why thenitrate concentration in the alumina boehmite is desirably 3.0 percentor less.

1. A process for producing a polymeric foam comprising the followingsteps: a. providing a foamable polymer composition comprising a blowingagent dispersed in a polymer matrix, the polymer matrix having asoftening temperature; and b. exposing the foamable polymer compositionwhile at a temperature at or above the softening temperature of thepolymer matrix to an environment having a pressure low enough to causethe foamable polymer composition to expand into a polymeric foam;wherein the foamable polymer composition further comprises aluminaboehmite dispersed in the polymer matrix.
 2. The process of claim 1,wherein the process is an extrusion process where the foamable polymercomposition is provided in an extruder at an initial temperature that isabove the softening temperature of the polymer matrix and at an initialpressure that precludes foaming of the foamable polymer composition andwhere step (b) occurs by expelling the foamable polymer composition toan environment having a pressure lower than the initial pressure andsufficiently low to cause the foamable polymer composition to expandinto an extruded polymeric foam.
 3. The process of claim 1, wherein thealumina boehmite is present in the polymer matrix at a concentration ina range of 0.1 to 30 weight-percent based on polymer matrix weight. 4.The process of claim 1, wherein the alumina boehmite has a nitrateconcentration of less than 3.0 weight percent.
 5. The process of claim1, wherein 50 weight-percent of all the polymers in the polymer matrixare alkenyl aromatic polymers.
 6. The process of claim 1, wherein theblowing agent comprises carbon dioxide.
 7. The process of claim 1,wherein the blowing agent comprises carbon dioxide and at least one ofiso-butane and water.
 8. A polymeric foam comprising a polymer matrixdefining a plurality of cells dispersed therein and further comprisingalumina boehmite dispersed within the polymer matrix.
 9. The polymericfoam of claim 8, wherein the polymeric foam is extruded polymeric foamthat is free of a network of polymer skins defining foam beads.
 10. Thepolymeric foam of claim 8, wherein the alumina boehmite is present at aconcentration in a range of 0.1 to 30 weight percent based on totalpolymer weight in the polymer matrix.
 11. The polymeric foam of claim 8,wherein the alumina boehmite is present at a concentration in a range of0.5 to 5 weight-percent based on polymer composition weight.
 12. Thepolymeric foam of claim 8, wherein the alumina boehmite has a nitrateconcentration of less than three weight-percent.
 13. The polymeric foamof claim 8, wherein more than 50 weight-percent of all the polymers inthe polymer matrix are alkenyl aromatic polymers.
 14. The polymeric foamof claim 8, wherein the alkenyl aromatic polymer is selected frompolystyrene homopolymer and styrenic copolymers.
 15. The polymeric foamof claim 8, wherein the polymeric foam has an open cell content of fivepercent or less.